Serena Williams orders espresso during Hopman Cup match

Female tennis champion world number one Serena Williams has downed an espresso mid match at the Hopman Cup in Perth, Australia this week, adding to her list of strange on court antics.

Williams requested a shot of espresso from the umpire following a first set defeat to Italian world number 12 Flavia Pennetta.

"I am a coffee drinker and I didn't have mine this morning and I was just feeling it," said Williams, in a statement. “So I had to get some coffee in me.”

The International Olympic Committee (IOC) removed caffeine from its list of banned substances in January 2004. According to the Institute for Scientific Information on Coffee (ISIC), any suggestions that caffeine’s short-term diuretic effect may impair physical performance are unfounded.

"I told them to just give me a shot of espresso. I asked them if it was legal; 'is it illegal to have a shot of espresso?' because I never did it before,” said Williams, in the statement.

A number of official sports bodies have reviewed the effects of caffeine on physical performance to determine whether it can be counted as an ergogenic aid.

The International Society of Sports Nutrition issued a position statement on caffeine supplementation and sports performance in 2010, which found that caffeine is effective for enhancing sport performance in trained athletes when consumed in low-to-moderate dosages.

Williams went on to raise her count of winning games to 15 in the second set.

"I needed some espresso. I needed to wake up – the jetlag gets you all the time,” she said, in the statement.

Williams said she was more worried about how the early morning rather than the heat was affecting her game, despite the fact that the temperature outside the Perth Arena, in Western Australia, had soared to 40 degrees.

"My gosh, hopefully I won't have any more (10am matches), or I will be pulling out… maybe a coffee sponsorship," she said, in the statement.